https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87744
--- Comment #13 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to Jakub Jelinek from comment #11) > Though, if it is common enough, one could try to optimize the __ll[0] == 0 > && __xx[0] == 0 case, one can do then either 32x32->64 or 64x64->64 > multiplication and be done with it. But if it is rare in random's usage, it > would just make the code larger. We will only use this new type when the calculation a*(m-1)+c doesn't fit in 64 bits, and the input values should be uniformly distributed in [0,m) for a good choice of parameters (and for a bad choice of parameters, you have bigger problems than the calculation being slow!) For a small value of a and large value of c we would use this new type but the multiplication step would overflow infrequently, but I don't think that's a good choice of parameters and not worth optimizing for. So I think we should just use the full 64x64 multiplication unconditionally. For operator% the if (__l._M_hi == 0) branch is probably worth it, because the general case is so much more expensive.
